About the same as Pikmin 3 and DKC: TF I think. Sadly.

Not many hit new franchises are born on platforms with this small of a userbase (selling less than the GCN).

Hopefully though Nintendo should have a Splatoon: Special Edition or Splatoon 2 ready for the launch of their next handheld (fusion?) device, maybe it can break out there.

Kinda like how Animal Crossing/Forest debuted on the N64 late in the N64's lifecycle and wasn't really a hit until the next system and not really a monster hit until its third instalment on the portable DS.

200-300k.

I am going to be brave and say that splatoon will be the next big franchise for nintendo. I predict 2-4 million.

25 years ago, as driving was one of the favourite genres in videogaming, Nintendo created a new driving game giving it the Nintendo touch. I bet many would say it wouldn't sell. Now every itineration sells millions and millions.
15 years ago, as fighting was one of the favourite genres in videogaming, Nintendo created a new fighting game giving it the Nintendo touch. I bet many would say it wouldn't sell. Now every itineration sells millions and millions.
In present day, as shooters is the favourite genre in videogaming, Nintendo is creating a new shooting game giving it the Nintendo touch. Many say it won't sell. Every itineration will sell millions and millions.

Of course it depends on many factors like many have referred in this thread, but I'm almost certain Nintendo will make it a success.

i dont know, i really want it to do well because ot looks a good game where once you get your head round tactics etc it could be fairly enjoyable (if in a good squad) with the whole person flying ahead and painting the paths and the other team causing ambushes in certain areas.

I really like the look of it and games like this will have me buying a wiiu one day (that day is getting very close) - i think no more than Pikmin 3 sales but i really do hope it will do better.

Also - there must be a way they can get 3DS play / some kind of commander mode or something involved as a companion app.

Many people keep using the "new IP" argument when giving a negative opinion on a game's prediciton thread, and I don't refer only to this one about Splatton, but many others about many other games. I fail to see exactly why being a new IP people believe it will sell less or it won't sell decently. Of course there are certain estasblished IPs that companies like to "milk" because they will sell so it's risk free. But new IPs to pretty well if the game is good:

- Arkham City sold just a little bit more than Arkham Asylum and we all have to agree that City was better than its predecessor;
- Resistence sold more than resistance 2 and 3 combined;
- The 1st Assassin's Creed is still the 2nd best selling out of the 6 ACs released for both PS3 and X360, and still pretty close to the best selling ones;
- Watch Dogs (need I say more?);
- Destiny (need I say more? Yes it will do very well)
- The original Gran Turismo for PS1 is still in 3rd place among all the GT itinerations released;
- All 3 Gears of war have very similar sales;
- etc

Bottom line, it depends on the quality of a game. If it's good it will sell. Sure sequels to already successful games are more likely to sell, yet in order to get a sequel the game's 1st itineration had to be successful has a new IP. Personally I like new IPs better, or at least sequels a few years apart.

Maybe 400k.

Just adding one more reasoning why I think it will sell. It's Nintendo's take on a game genre that every other gamer nowadays likes, so it will attend to everyone's taste (those who own a WiiU that is). Since E3 this game is on everyone's radar and lots of non-Nintendo loyals are curios about this game. Pikmin 3 or Donkey Kong TG, for instance, don't cater to other gamers aside from Nintendo fans as much as Splatoon does.

Believe me, it will sell.

I'm thinking around 750k. It all depends on the marketing though, and Nintendo hasn't been good at for many years now.

Are you sure about that? I don't see much interest for the game outside of Nintendo gamers. As for DK:TF and Pikmin, well.. the same thing can be said can be said about this game. In fact, I don't know why DK:TF sold as much as it did on Wii U. As a well establised IP that sold well over 6 million copies (DK: Returns) last gen, it sure did drop off a lot.

To OP, I'm thinking about 450K.